Non riesco a farla funzionare...:

codice:
<html>

<head>
<script language="JavaScript"> 
<!-- 


var difference = function(leftHour, rightHour){
	if(!leftHour || !rightHour)
		return null;
	spt = leftHour.split(":");
	var totLeft = parseInt(spt[0]) * 60 + parseInt(spt[1]);
	spt = rightHour.split(":");
	var totRight = parseInt(spt[0]) * 60 + parseInt(spt[1]);
	return totLeft - totRight;
}

function Calcola()
{

	var diff1 = difference(myForm.F.value, myForm.E.value);
	var diff2 = difference(myForm.D.value, myForm.A.value);
	var diff3 = difference(myForm.G.value, myForm.F.value);
	var diff4 = difference(myForm.H.value, myForm.G.value);
	var diff5 = difference(myForm.H.value, myForm.A.value);
	
	myForm.RISULTATO1.value = diff1
	myForm.RISULTATO2.value = diff2
	myForm.RISULTATO3.value = diff3
	myForm.RISULTATO4.value = diff4
	myForm.RISULTATO5.value = diff5
    

}
// -->
</script>

</head>
<body>

<form name="myForm">

A<input type="text" name="A" size="20">
B<input type="text" name="B" size="20">
C<input type="text" name="C" size="20">
D<input type="text" name="D" size="20">
E<input type="text" name="E" size="20">
F<input type="text" name="F" size="20">
G<input type="text" name="G" size="20">
H<input type="text" name="H" size="20">




  
F-E<input type="text" name="RISULTATO1" size="20" onClick="Calcola()">
D-A<input type="text" name="RISULTATO2" size="20" onClick="Calcola()">
G-F<input type="text" name="RISULTATO3" size="20" onClick="Calcola()">
H-G<input type="text" name="RISULTATO4" size="20" onClick="Calcola()">
H-A<input type="text" name="RISULTATO5" size="20" onClick="Calcola()">


</form>

</body>

</html>